In order to increase the power reserve, by increasing the number of turns of a mainspring, one solution consists in decreasing the diameter of the barrel arbour and of the associated core, so as to increase the space available for the spring inside the drum.
The ratio of the core radius to the spring thickness is usually comprised between 10 and 20 and the invention proposes to reduce this ratio to below 10, and preferably to within a range of between 5 and 10.
The sizing must not be too small; there is a risk of breakage if the core diameter is too small.
In the conventional barrel architecture, a ratchet is axially mounted on a barrel arbour or on a core, via a square, with the ratchet usually being secured by an axial screw. The dimension of this screw and that of the square thus define the minimum diameter of a pivot shoulder. A step portion joined to this pivot shoulder limits the endshake of the arbour or of the core relative to a bottom plate or to a bridge carrying a jewel or similar element.
An even larger diameter than that of the step portion is required for a shoulder for guiding the pivoting of the drum on the arbour or on the core, combined with a step portion limiting the endshake of the drum. The dimension chain required to observe minimal sections of material results in substantial dimensions, which are difficult to reduce. In particular, it is not sufficient merely to reduce all of the dimensions, since the cross-sections of material are then insufficient to ensure fatigue resistance.
FR Patent No 2287717A1 in the name of SCHILD discloses a barrel with a ratchet wheel fixed to the arbour and adjacent to the bridge 10A in which the arbour pivots. The barrel includes a single-piece click, formed of a rigid part rotatably movable about the arbour between a locking position and a release position, and a resilient arm whose free end has a locking beak able to engage in the ratchet toothing. The click is housed inside a recess in bridge 10A between bridge 10A and the ratchet wheel. The free end of the arm has a bearing element located inside the contour of the ratchet, the flanks of this recess include two stop members one of which cooperates, in a locking position, with the bearing element and the other with the locking beak, to determine the locking position
FR Patent Application No. 11371491 A in the name of PONS discloses a lubrication method and device. The ratchet fixed to the barrel arbour has access apertures on one portion of barrel bridge 10A or on one portion of the top barrel bearing. Bridge 10A may have similar apertures, as does the main plate for access to the cover bearing.
US Patent Application No. 886196A in the name of FALLER LEWIS ALBERT describes a barrel where the barrel drum and cover pivot in a limited manner via the walls of a cavity formed by a plate and a bridge 10A pressed against each other. The drum pivots about the barrel arbour via a ring which includes two flat portions which cooperate with an oblong hole in the drum. This ring carries the ratchet via a screw thread and the ratchet pivots in a limited manner via the walls of a cavity defined by the main plate and the drum. On the opposite side, the arbour carries a wheel between the cover and bridge 10A.
CH Patent Application No 295135A in the name of BRAC discloses a barrel wherein the core carries the ratchet, whose motion is limited by a thread on the plate. This core pivots on an arbour, one end of which cooperates with a bore in the plate, and the other end of which includes a screw thread. This screw thread cooperates with the inner thread of a centring case mounted in a bore in bridge 10A. The screw thread and the support plate hold a centring ring forming a stop member for the end of the core on the side of bridge 10A.
EP Patent Application No 2196866A2 in the name of HORLOGERS SARL concerns a bayonet device fixing the ratchet to an end square of the arbour. It combines a non-circular drive profile at the end of the arbour, which is separated by a groove from a stepped portion for the abutment of the ratchet. The ratchet includes a cutout part of complementary shape to the non-circular drive profile, onto which it is fitted and then placed in abutment on the collar. A securing washer includes a cutout part of complementary shape to the non-circular drive profile of the arbour, onto which it is fitted. This washer is then screwed onto the ratchet by at least one eccentric screw.
JP Patent Application No 11183644A in the name of SEIKO INSTR INC concerns a barrel which includes, for displaying the power reserve of the barrel, the use of the drum as a planetary wheel holder, which holds a planetary wheel pivotally mounted on the base thereof. The plate of this planetary wheel meshes with a wheel coaxial to the barrel arbour, whereas its pinion meshes with a solar wheel, also coaxial with the barrel arbour, axially retained by a stop. The solar wheel meshes with a wheel of a gear train pivoted on the main movement plate.
US Patent Application No 820252A in the name of PORTER WILSON discloses a barrel arbour with a hook on a median shoulder of large diameter, and a recess in front of the hook for the mainspring.